Seeing that it's a Dell, have you also installed the Resource/Drivers CD that might be included in the package? If not, please do so.. If there is no such Drivers CD, then you'll need to visit the Dell site and download, then install all the appropriate hardware drivers.. Chipset, audio, video, ethernet, etc.
Hope this helps.
I had to reformat my hard drive and reinstall XP MCE 2005 on my Dell XPS 400, using the reinstallation DVD. But now there are two problems. First, there is no sound, despite Device Manager showing "audio codecs." Second, an attached ethernet cable is not recognized, and Device Manager shows a yellow exclamation mark (no driver) for "Ethernet Controller," as well as for PCI Device, PCI Simple Communications Controller, SM Bus Controller, Unknown Device, and Video Controller (VGA Compatible). So I cannot connect to my router and get online. Thanks.